Ask Anything - July 2014

Michael Zehl; via CarCraft@CarCraft.com: I recently read the EFI test article in the Mar. '14 issue of Car Craft. I found the article incredibly informative. I am planning an EFI swap on my '78 Trans Am barn find. I had been struggling with which one to choose. I am left with one question your article did not cover: How well does each of these units fit underneath a stock air cleaner? My TA with a shaker scoop leaves no room for any spacers of any kind. It is currently running a Pontiac 400 with a mild cam, Edelbrock Performer manifold, and a Q-jet carb. It fits the height of my hood perfectly. I think your article covered the systems very well, except on this part, and I was very happy to read it. If you have any information that may guide me in my selection process, it would be greatly appreciated.

Jeff Smith: Great question, Michael—had we thought of it, we would have given you the specs. We still have all these systems, so we measured each throttle body from the base where it bolts to the intake manifold to the ring that mounts the air cleaner. First, we started with a standard square-flange Holley carburetor, a Rochester Q-jet, and then all of the EFI throttle bodies, including the Professional Products unit. As you can see, nearly all the throttle bodies will probably work, with the possible exception of the FAST EZ-EFI 2.0, although 0.060 inch is probably not going to cause a major problem. We used a drop-style, air-cleaner base on our big-block test Nova to help clear the stock hood, and none of the throttle bodies caused any fitment problems, although the EZ-EFI 2.0 was a little tight to the air-cleaner base in one spot. In the past, we have had fitment issues with a short throttle body where the throttle linkage hit the base of the air cleaner at roughly three-quarter throttle, but we minimized this problem with an extra gasket between the throttle body and the air-cleaner base.

2/4The Holley throttle body is the shortest of all the units we measured, and therefore would offer the most hood clearance to the air cleaner.

Brody Malsom; via CarCraft@CarCraft.com: Hey guys, great mag. I've been reading and learning so much from your articles in the past five years I've been subscribing. I'm 18 and in my senior year in high school, and my buddy and I bought a '66 GMC pickup together. We are going to ditch the tired V6 for a 383 stroker. As of now, the block has been bored 0.030 inch, and we have a Scat series 9000 stroker kit on the way for it. My question is what cylinder heads would be the best for us since we're not trying to make a butt ton of power and not spend an arm and a leg on this build. I have experience with rebuilding engines, but as for this stroker combo, I have no idea where to start when it comes to looking for heads that will make decent power. Also, I was wondering about the cam—again, I have no idea where to even begin. I appreciate your time and look forward to your advice. Thanks for all the great info and knowledge.

Jeff Smith: We always try to help out the younger readers, since they are going to be the ones to continue our hobby/sport, so let's take a shot at your question, Brody. Assuming that you purchased the entire Scat 9000 rotating assembly, you didn't mention what piston came with the system. We looked at prices at SummitRacing.com, and we'll also guess that since you are a high school student that you went with the least-expensive kit that features a hypereutectic flat-top piston with 5cc piston valve reliefs. While the longer 3.75-inch stroke creates additional displacement, it also has a direct effect on increasing compression ratio, assuming all other components remain the same. As an example, with a 355ci engine with a 3.48-inch stroke, a flat-top piston with 5cc valve reliefs, a 64cc combustion chamber, 0.041-inch-thick head gasket, and a 0.015-inch piston-to-deck height will deliver a 10.0:1 compression ratio. But change the stroke to 3.75 inches (all other specs remaining the same) and compression jumps to 10.7:1. So the piston style has a significant effect on what we can now suggest for a cylinder head.

Let's assume that you went with the less-expensive flat-top piston kit. This means we need to look for a cylinder head with a minimum 70cc chamber to keep the compression pump-gas friendly. Because this will be a street truck, we should also keep the cam timing conservative. This will work better with a budget cylinder head, but short intake duration numbers also affect the compression. As you can see, all these factors are interrelated. We really need to keep the compression around 9.5:1 so the motor is still snappy and responsive, yet doesn't build excessive cylinder pressure so that it detonates. Let's first take a look at the cylinder heads because once we select a head, this will help determine the cam timing.

Cylinder heads are the big determiner of power. A stock replacement iron head will be the cheapest, but frankly this will limit both torque and horsepower. I found an interesting 72cc combustion chamber iron head from Summit Racing. This is more of a stock replacement head with a 165cc intake port, 2.02-/1.60-inch valves and screw-in, 3⁄8-inch studs with stock 1.25-inch-diameter single valvesprings. I don't know much about these heads, except that they are certainly priced attractively at $635 for the pair. You really can't properly rebuild a set of used stock iron castings for much less than that. With a 72cc chamber and a flat-top 5cc piston, this would place static compression at 9.84:1, which is a bit high but still workable. This assumes the piston is 0.015 inch below the deck surface.

If by chance you are using a dished piston, then a 64cc combustion chamber is a better way to go since that will keep the compression in the neighborhood of 9.5:1 to 9.8:1 with a 13cc dish. If that's the case, then the Chevy iron Vortec head is a great selection. This is the best-flowing production iron head for the small-block Chevy, developed for truck engines from 1996 through 2000. It has good port flow for a small production head, but the exhaust port is its Achilles' heel. But it will still make excellent torque and decent horsepower on a 383. Back in the Dec. '04 issue (“Torque Tales”), we built a 383 with Vortec heads and an Isky 221/232 cam with 0.496-/0.517-inch lift. We used a set of conical Pioneer springs to allow that much lift (the stock heads are limited to a maximum of 0.450 inch lift), but the engine responded with 444 lb-ft of torque at 3,600 and 375 hp at 5,400 using a 1.6:1 rocker to help the lift. This was with headers, an Edelbrock Performer RPM Air Gap Vortec manifold, and a 750-cfm carburetor. Remember that the Vortec requires its own specific intake manifold bolt pattern. A stock Chevy bolt-pattern intake will not fit the Vortec heads. The Vortec head means added expense for a Vortec-style manifold.

If you have a little bit more money to spend on a set of aluminum cylinder heads, we tested the Speedway Motors aluminum heads as part of Car Craft's budget cylinder head test in the Sept. '12 issue—you can find that complete story on Car Craft's website. The Speedway heads made 381 hp on our Saturday Night Slayer test 355. We also tested the iron Vortecs on that engine, and they made 378 hp and 408 lb-ft of torque. The aluminum Speedway heads got the nod for average horsepower per dollar, where we took the price of the heads and divided it by our test engine's average horsepower. When we tested these heads, they sold for $739.98 for the pair and were the least expensive heads that still made decent power. This, however, is also a 64cc chamber head. Looking at larger chamber heads, we found a set of 70cc chamber Edelbrock E-Street aluminum heads on Scoggin-Dickey's website that we also tested in our head comparison. These heads made 395 hp on our 355 Slayer engine and offer the virtue of being cast and machined in America. Our original price as tested in the story was $909, but our latest search found the price actually lower at Scoggin-Dickey at $854, which was a nice surprise. This is an outstanding price for a quality head.

We alluded to cam timing in the Vortec head previous test example, and the cam we employed in our cylinder-head test is also relevant. The cam we chose was a Summit brand hydraulic flat-tappet cam measuring 224/234 degrees at 0.050 with 0.465/0.485 lift, but we enhanced it with a set of 1.6 roller rockers to bump the lift up to 0.496 and 0.517. This cam has a lobe-separation angle (LSA) of 114 degrees that reduces the overlap and calms the idle characteristics. Since you are young and probably want a little bit more lump to the idle, you might look for a cam with a tighter LSA angle. What this refers to is the amount of time (in degrees of duration) the closing exhaust valve and the opening intake valve are simultaneously open. A tighter LSA angle of 110 degrees means the exhaust valve closes a little bit later and the intake valve opens a little bit earlier, which increases the overlap. This directly impacts idle quality by decreasing intake manifold vacuum. This makes the idle a little lumpier. This also tends to bleed off a little cylinder pressure at low engine speeds, which can make the engine a little less sensitive to changes in ignition timing. This allows you to run a little more timing at low speeds to improve throttle response and low-speed torque.

Note that the cam we chose was what's called a dual-pattern cam. This means the cam includes more duration on the exhaust lobe than on the intake lobe. This is important, especially when using stock or stock-type cylinder heads. The small-block Chevy generally has a somewhat weak exhaust port relative to intake port flow. Even below 6,000 rpm, that peak horsepower is affected by the exhaust port's inability to scavenge the cylinder of most of the combusted material. This leaves some exhaust gas remaining in the cylinder, which does a great job of reducing net power in the next four-stroke cycle. By increasing the duration on the exhaust side, this gives the exhaust port a little more time (degrees of duration) to vent more of the remaining exhaust gas out of the cylinder. This usually results in making a little more peak horsepower. So look for a cam with around 220–226 degrees of duration at 0.050 with a little more duration (230–236 degrees) on the exhaust side. This will be a good cam timing package for a mild street engine with compression around 9.5:1. Be sure to use high-quality break-in oil when you start the engine for the first time. We did a specific camshaft break-in story that you can find online at CarCraft.com that goes into specific recommendations that will help you with the initial fire-up so that you don't lose a cam lobe due to improper lubrication.

4/4The Edelbrock E-Street head is a good choice for a budget small-block. You can find more information on this head in our budget cylinder head test from the Sept. ’12 issue. Just search for “Car Craft budget cylinder head test” on CarCraft.com.